The present invention relates to a spinel type ferrite film high in the utility value in particular in high frequency magnetic devices such as, inductance elements, impedance elements, magnetic heads, microwave elements, magnetostrictive elements and electromagnetic interference suppressors that are used to suppress electromagnetic interference owing to the unnecessary electromagnetic waves in a high frequency region and a manufacturing method thereof.
In a ferrite plating process, as mentioned in Japanese Unexamined Patent Publication No. S59-111929 (hereinafter referred to as “literature 1”), an aqueous solution containing at least ferrous ion as a metal ion is brought into contact with a solid surface, thereby Fe2+ alone or both of Fe2+ and another metal ion are allowed to be absorbed on the solid surface, subsequently the absorbed Fe2+ is oxidized and thereby Fe3+ is obtained, this causes a ferrite crystallization reaction with the metal ion in the aqueous solution, and thereby a ferrite film is formed on the solid surface.
So far, there are various processes that are proposed based on the above process: one that intends to homogenize a ferrite film and improve a reaction rate (for instance, Japanese Unexamined Patent Publication No. S60-140713 (hereinafter referred to as “literature 2”)), another one that intends to form a ferrite film on various solids by endowing a solid surface with the surface activity (for instance, JP-A No. 61-030674 (hereinafter referred to as “literature 3”)), and still another one that intends to improve the formation rate of a ferrite film (for instance, Japanese Unexamined Patent Publications Nos. S61-179877 and S63-42378, and JP-A No. 02-116631 (hereinafter referred to, respectively, as “literature 4”, “literature 5” and “literature 6”)).
In the ferrite plating, as far as a solid on which a ferrite film is intended to form is resistant against the aqueous solution, any solid can be used. Furthermore, since it is a reaction through an aqueous solution, an advantage is made in that a spinel type ferrite film can be formed at a relatively low temperature between room temperature and a boiling point or less of the aqueous solution. Accordingly, in comparison with other processes of forming a ferrite film, a limiting range on the solid is smaller.
In order to improve the characteristics of such ferrite films, various trials have been attempted.
For instance, Japanese Unexamined Patent Publication No. H02-116624 (hereinafter referred to as “literature 7”) discloses a method in which with paying attention to an improvement in the magnetic characteristics of a ferrite film, the ferrite plating is carried out in a magnetic field, and thereby the soft magnetic characteristics are improved.
Furthermore, JP-A No. 3-38006 (hereinafter referred to as “literature 8”) proposes a method in which a solution containing at least ferrous ion is brought into contact with a substrate in a magnetic field, the ferrite plating is applied on a solid surface in a magnetic field, and thereby a ferrite film having the uniaxial anisotropy is obtained; and a method in which an oxidant is contained in a solution to oxidize ferrous ion.
Still furthermore, JP-A No. 60-202522 (hereinafter referred to as “literature 9”) discloses that when attentions are paid to a composition of ferrite and a weight ratio of Co/Fe in a film is set in the range of from 0.001 to 0.3, excellent magnetic characteristics can be obtained.
According to the literature 6, it is proposed to repeat a step in which after a reaction solution containing at least ferrous ion is brought into contact with a substrate, a solution containing at least an oxidant is brought into contact with the substrate, and thereby to form a ferrite film on a surface of the substrate; and it is said that thereby a formation rate of the ferrite film can be improved.
However, in the literature 6, no clear mention is made of a step of removing the reaction solution containing at least ferrous ion and the solution containing at least the oxidant.
Furthermore, a method is proposed in which a ferrite film is formed on a substrate having the center line average roughness Ra of 0.01 μm or more (for instance, JP-A No. 1-246149 (hereinafter referred to as “literature 10”)).
In the case of the literature 10, in an embodiment thereof, it is disclosed that when a ferrite film is formed on a substrate having the center line average roughness Ra in the range of from 0.01 to 0.8 μm, a homogeneous film free from irregularity in a thickness can be obtained.
However, the ferrite films according to the above-mentioned existing processes, in view of applying to an inductance element, impedance element, magnetic head, microwave element, magnetostrictive element and electromagnetic interference suppressor in a high frequency region, are insufficient in the soft magnetic characteristics. Accordingly, a large problem existed as to applications or adaptations to various kinds of electronic components and so on. In order to overcome the problems, specifically, imparting a film a magnetic uniaxial anisotropy, optimizing a chemical composition of the film, and homogenizing the film become important points.
A film that is manufactured according to a general ferrite plating process (for instance, literature 1) does not have the magnetic directivity (isotropic); accordingly, when a constituent element of a ferrite film has the uniaxial anisotropy and the magnetic permeability thereof is assumed to be A, the magnetic permeability of as a whole film becomes about A/2 and excellent potential in the soft magnetic characteristics that the ferrite film intrinsically has cannot be extracted. Furthermore, in the case of a ferrite film that has the uniaxial anisotropy such as disclosed in the literature 8 being used in an inductance element, when for instance a spiral coil is used, a problem exists in that owing to the anisotropy of the magnetic film a portion where the magnetic flux density is locally lowered is generated inside of the element, as a result an inductance as a whole is lowered.
Furthermore, as mentioned above, various improvements have been proposed to improve a formation rate of a ferrite film; however, from an industrial productivity point of view, these are insufficient; accordingly, a large problem has been remained in the applications to various kinds of electronic components or in the adaptability thereto.
Still furthermore, in the above literatures 7 and 8 that pay attention to an improvement in the magnetic characteristics, in an embodiment that is a specific explanation thereof, there is a description that “a plating solution can be separately supplied”; however, all embodiments in, for instance, the literature 8 adopt a method in which a plurality of plating solutions is mixed before the ferrite crystallization and supplied to a substrate. Accordingly, it is supposed that because fine ferrite grains that are secondarily formed other than on a solid surface disturb the crystal growth or Fe2+ is unevenly absorbed on a solid surface, a ferrite film that is an aggregation of homogeneous grains is obtained with difficulty.
Furthermore, the literature 9, though paying attentions to relationship between compositions and the magnetic characteristics, aims usage as magnetic recording media, intends to realize higher coercive force and higher residual magnetic flux density, but does not relate to a ferrite film that is used in an inductance element, impedance element, magnetic head, microwave element, magnetostrictive element and high frequency magnetic device; that is, the literature 9 is a technique that relates to one that is obviously different in the characteristics required for high frequency magnetic devices such as an electromagnetic interference suppressor that is used to suppress electromagnetic interference owing to unnecessary electromagnetic waves in the high frequency region.
On the other hand, in the case of the technique by which a ferrite film is formed on the above-mentioned substrate, in view of applications to recent magnetic devices, a magnetic substance that is used therefor, in the magnetic characteristics thereof, is necessary to be high specifically in the magnetic permeability. In order that a film that is obtained by the ferrite plating process may have high magnetic permeability, control of a composition of a film, in particular control of crystal orientation of grains that form the film is indispensable.
However, according to the above-mentioned existing processes, in all of the processes, a technique for controlling the crystal orientation that takes correlation with the magnetic characteristics into consideration is not introduced (that is, for instance, in the literature 10, no mention is made of correlation between the center line average roughness Ra of the substrate and the crystal orientation and the magnetic characteristics of the film; in the literature 3, there is described that in order to supply a homogeneous film excellent in the adhesiveness, a surface of the substrate is necessary to be plasma treated; furthermore, in the literature 7, the magnetic characteristics of a film that is obtained are taken into consideration, however no mention is made of steps of removing the reaction solution and the oxidizing solution and the correlation between the crystal structure and the magnetic characteristics of the film of the substrate and the surface roughness of the substrate); as a result, a problem exists in that high magnetic permeability cannot be obtained.
In the case of the ferrite film particularly due to the ferrite plating process, as mentioned above, the ferrite film is formed through crystal growth from a starting point on the surface of the substrate; however, according to the existing processes, since fine ferrite grains secondarily formed other than on the surface of the substrate disturb the crystal growth or Fe2+ is unevenly absorbed on the surface of the substrate, the crystal orientation can be controlled with difficulty (for instance, as in the literature 10, when a ferrite film is formed on a surface of a substrate that is extremely small in the center line average roughness Ra, a homogeneous film can be obtained with difficulty, and the crystal orientation can be controlled with difficulty). As a result, in spite of various improvements so far being proposed to improve the formation rate of the film, these improvements are insufficient from a viewpoint of the industrial productivity. In addition to the above problem, there is a large technical problem in that when applying to the magnetic devices and adapting to various kinds of electronic components, high magnetic permeability cannot be obtained.